Specifically, Twitter has a feature -- actually pretty useful --
that lets you receive private direct messages on your phone via
SMS text message. This is a handy way of using Twitter as a
real-time, private messaging system -- sort of what SMS was
designed for.

Here's how it works: If someone direct messages ("DMs") you on
Twitter, you'll get a text from 40404 (Twitter's SMS shortcode)
that says something like "Direct from fromedome," with the
message included.

The problem is that many people respond to those text messages
the same way they respond to any other text messages: With a
private message intended for the person who messaged them.

But that's not how Twitter's SMS system works -- it treats that
as a public tweet, and publishes it for everyone to see.
If you want to send a direct message reply, you have to
remember to type in "d username" before the message.
Every time. Twitter doesn't think about this for you.

The result is that every day, we see "accidental DMs" or "DM
fail" tweets "via txt" that are clearly meant to be direct
messages. (And not just by new Twitter users, but usually by
long-time users. This is clearly something that people can't
quite fully learn and remember.)

We don't usually know who the messages are meant for, and often
they're mundane or harmless. But every few days, we see
something embarrassing.

If you don't mind the occasional accident, and have nothing to
hide, go ahead and keep the DM-to-SMS feature turned on.

But if you want to make sure you never screw up, here's how to
turn off this feature: Go to Twitter's mobile device settings
(you'll need to sign in) and under "Text message notifications,"
uncheck "Direct messages."

It would be nice if Twitter figured out a solution to this
problem, because it's actually quite handy to have DMs turned on
via SMS. But we doubt that's a priority for the company. So for
now, the best way to protect yourself from accidentally tweeting
direct messages is to turn off the feature completely.